1. Field of the Invention
The invention relates generally to current limiting circuit interrupters and, more particularly, to molded case circuit interrupters having a magnetic arc stretcher.
2. Description of the Prior Art
Circuit breakers are widely used in industrial, commercial, and residential environments to protect power distribution equipment against damage from overcurrent conditions. Such circuit breakers have traditionally employed spring-loaded operating mechanisms which provide for manual opening and closing of the contacts therein, and a trip mechanism responsive to overload current conditions for releasing a latch to allow the operating mechanism spring to automatically separate the contacts.
As the capacity of supply circuits increased to accommodate the ever higher consumption of electrical energy, larger fault currents became available to flow under short circuit conditions. In order to properly protect against these higher available fault currents, current limiting devices were employed to prevent short circuit current from rising to the level of the full available fault current. Although the earliest current limiting systems employed separate units connected in series with conventional circuit breakers, there is an increasing trend to combine current limiting capabilities and standard overload circuit interrupting capabilities into a single device.
One method of obtaining current limiting in a mechanical circuit breaker is to provide means for rapidly separating the contacts a long distance upon detection of short circuit conditions, drawing an extended arc therebetween. The relatively high voltage developed across the long arc opposes the rise in short circuit current flow. Although considerable success has been achieved through this method, the size limitations of smaller rating circuit breakers, especially molded case circuit breakers, has restricted the available contact separation distance and, therefore, the arc voltage which can be developed.
Another means of obtaining a high arc voltage to produce effective current limiting action is to magnetically stretch the arc to provide an arc path longer than the contact separation distance. An example of a circuit interrupter employing magnetic means to stretch the arc is described in U.S. Pat. No. 2,734,970, issued Feb. 14, 1956 to Neilus A. Spears, Jr. and assigned to the assignee of the present invention. The circuit breaker described therein is a high power direct current circuit breaker operating at a potential of 1,000 volts. It would be desirable to provide a circuit interrupter employing a magnetic arc stretcher which is suitable for use in applications requiring a molded case circuit breaker.